The present invention relates to the production of building materials and, more specifically, to cements and processes for producing same.
Cements consisting of highly-basic calcium silicate (alite), calcium orthosilicate (belite), calcium aluminate and calcium alumoferrite are known. In the stage of preparation of grouts and concretes, cements are added with chlorides, mainly calcium chloride, to speed up the process of cement hydration and intensify hardening of said grouts and concretes at both negative and positive temperatures.
A process for producing the above-described cements which is known in the art comprises calcination of a raw mixture consisting of calcareous, silicaceous, aluminous and ferrous components at a temperature within the range of from 1,400 to 1,450.degree. C, followed by grinding of the resulting cement clinker. In the stage of preparation of grouts and concretes, the cements are added, for the above-mentioned purpose, with chlorides, mainly calcium chloride.
The prior art cements have a low hydration speed at low positive (0 to 5.degree. C) and negative (down to -20.degree. C) temperatures. To speed-up the process of cement hydration at said temperatures, cement is added, during the preparation of grouts and concretes, with chlorides such as calcium chloride. With increasing amount of chlorides, the effect produced thereby in concretes or grouts is also increased. Therewith, however, corrosion of steel reinforcement in said concretes and grouts is more pronounced, especially during heat-humid treatment of the latter. This restricts the amount of the chloride additives to the range of from 2 to 2.5% by weight of the cement under normal conditions of hardening of concretes and grouts or 1 to 1.5% by weight of the cement in the case of heat-humid treatment of said concretes and grouts.
A disadvantage of the prior art process for producing said cements resides in a high calcination temperature causing great consumption rates of the fuel. Furthermore, the cement clinker produced at this temperature has a low grinding ability, resulting in increased power consumption for such grinding.